Answer:
I promise to be true to you - This means being there for the other and always telling the truth. Also acting in truth. I think it is very important in marriage.
In good times and in bad - Most marriages end because of the bad times. Being true to the other during the rough times is very important because you must have patience.
In sickness and in health - When your spouse becomes ill, you need to be there for them to comfort and support them. I believe that true love is shown by simply being there and comforting your spouse no matter the rough patch they may be in.